Electrowetting display devices are known. In an off state of a known electrowetting element an oil layer covers a display area. In an on state the oil layer is retracted so as to cover less of the display area. To switch the electrowetting element to the on state a voltage is applied via an electrically conductive fluid immiscible with the oil. To switch the electrowetting element to the off state, the voltage is switched off. By switching the oil and the electrically conductive fluid to different fluid configurations, different optical states can be displayed by the electrowetting element.
It is known to control the movement of the oil and the electrically conductive fluid for example by providing a surface in the electrowetting element with a different wettability for the oil than for the electrically conductive fluid or by appropriately selecting the shape of the electrowetting element to cause a preferred direction of motion of the fluids upon application of a non-zero voltage.
It is desirable to provide improved techniques for fluid motion control in an electrowetting element.